1. Field of Invention
The present invention relates to a dot inversion system of displays, especially to a polarity switching member of a dot inversion system.
2. Description of Related Art
Due to fast development of modern technology, manufactures of information products bring out more and more products to satisfy various requirements of people. In early days, most of the displays use Cathode Ray Tubes (CRT). The CRT has shortcomings of large volume, high power consumption and the radiation that may have effects on human health after long term use so that it is gradually replaced by liquid crystal display (LCD) that has compact volume, low radiation and low power consumption. Therefore, the LCD has become the mainstream on the market.
The liquid crystal material used in the Liquid crystal displays has different refractive indexes and dielectric constants. The difference of the refractive indexes leads to polarization change ability of the liquid crystal and the difference of the dielectric constants results in various rotation angles of liquid crystal under the influence of the electric field. Thus by change of the refractive index in combination with polarizers, the amount of light passes can be controlled. The liquid crystal itself is not conductive while positive charge and negative charge in the liquid crystal are separated from each other. Once an electric field is applied, the liquid crystal molecules aligns and under control of the electric field. Moreover, when a direct current field is applied across, the charges in the liquid crystal molecules are fixed and the liquid crystal molecules posses dipole moments. This leads to late response of the liquid crystal molecules. Thus an alternative current is use to drive the liquid crystal molecules. Once there are some residual charges from direct current in the liquid crystal molecules, the cell response of the liquid crystal molecules is delayed while changing the tilted angle of individual liquid crystal molecules. This causes image sticking and flicker. The liquid crystal modules include liquid crystal molecules filled between an upper polarizing filter and a lower polarizing filter. When being applied with an alternative current, directions of the electric field between the upper polarizing filter and the lower polarizing filter changes alternatively. The AC driving method of liquid crystal displays includes four types-Frame Inversion, Line Inversion, Column/Data/Source Inversion, and Dot Inversion.
Generally, the liquid crystal displays use line inversion and dot inversion. Refer to FIG. 1A & FIG. 1B, a schematic drawing showing a line inversion system of a conventional technique. As shown in figures, a driving way of the line inversion is that each horizontal line (a line of liquid crystal cells) has opposite polarity as compared to its direct neighbor while driving the liquid crystal molecules. Now the signal change frequency of the common electrode is a half of the horizontal scanning frequency (Horizontal Scanning Frequency/2). The horizontal scanning frequency is the number of horizontal lines scanned by the electron beam in a television receiver in 1 second. The polarity change frequency of each horizontal line is the same with that of the frame inversion-a half of the vertical scanning frequency. The flicker frequency of each horizontal line is the same with the flicker frequency of the frame inversion. Because that each horizontal line has opposite polarity as compared to its direct neighbor at any time, the liquid crystal molecules in the vertical direction have high-frequency polarity change. Such way can reduce the flicker.
Refer to FIG. 2A & FIG. 2B, a schematic drawing showing polarity switch member of a dot inversion system of a conventional technique. As shown in figures, a driving way of the dot inversion is that each liquid crystal cell has opposite polarity as compared to the surrounding neighbors. The dot inversion can be considered as a combination of the line inversion and the Column/Data/Source Inversion. The disposition way of the source driver chip of the dot inversion is the same with that of the line inversion. The polarity of the output signal of the upper source driver chip is opposite to that of the lower source driver chip. The signal polarity changes once per a horizontal scanning cycle. After a vertical scanning cycle, the signal polarity changes again. The switching frequency of polarity of each liquid crystal cell is maintained at half of vertical scanning frequency. Each of the liquid crystal cells in the vertical direction and in the horizontal direction has different polarity. Under high switching frequency of the polarity of the liquid crystal cells in the vertical and horizontal directions, the images have good average effects and the flicker is further eliminated.
However, driving chips in small-size Thin-Film Transistor Liquid-Crystal Displays can be driven only by line inversion due to constraints for manufacturing processes. The line inversion way may have display flicker effects. For the Thin-Film Transistor Liquid-Crystal Displays, the dot inversion can eliminate the flicker effect. In order to achieve dot inversion, the voltage difference of the source driver output ranges from 10 to 12 volt. Yet the withstand voltage of the middle voltage components produced by the mass-production processes available now are only 5˜6.5 volt and are unable to be applied with dot inversion that requires 10˜12 volt.
Thus there is a need to provide a novel polarity switching member of a dot inversion system that the component with withstand voltage of about 5 volt can achieve 10 volt voltage difference by switching of voltage polarity of the P-well and the N-well so as to drive the display panels.